The present invention relates to a curable resin composition. More specifically, the present invention relates to an electroconductive curable resin composition and a cured (or hardened) product thereof having not only excellent electroconductivity but also an excellent heat-radiating property.
The pace of recent technological innovations in the electronics industry, etc., is remarkable, and materials technology supporting the electronics industry is also making rapid progress. The same applies to the development of polymer materials and a large number of novel or high performance polymer materials have been newly developed and have individually expanded their range of uses in a steady manner.
The principal properties required for the polymer materials in the field of electronics are formability, heat resistance, durability, electrical characteristics (e.g., high insulation, high electroconductivity), corrosion resistance, heat-radiating property and the like, though these properties may vary depending on the products or uses. In many cases, for such purposes, there are used thermosetting resins represented by epoxy resins, phenolic resins, etc., or various engineering plastics represented by polyimides, polycarbonates, polyphenylene oxides and liquid crystal polymers, etc.
The demand for a material comprehensively having all of the above-mentioned various performances is of course strong, but great difficulties are present for realizing such a polymer in view of the techniques to be used therefor, and often disadvantageous results appear in view of the cost thereof. One of the technical requirements is to develop a polymer material having electroconductivity (particularly, high electroconductivity such that the volume resistivity is 1 xcexa9cm or less) and at the same time a having heat-radiating property and heat resistance. It is an object of the present invention to develop such a material. More specific examples of the above material may include a highly electroconductive composition for use in various members to be used in the field of batteries, such as separators for fuel cells using hydrogen, alcohol or the like as the fuel therefor.
Many studies have been made in the past on highly electroconductive compositions comprising a carbonaceous material and a thermosetting resin composition. For example, a combination of graphite and a phenolic resin is disclosed in JP-B-50-11355 (the term xe2x80x9cJP-Bxe2x80x9d as used herein means an xe2x80x9cexamined Japanese patent publicationxe2x80x9d) and JP-A-59-213610 (the term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d). Also, in the case of using an epoxy resin and an unsaturated polyester resin as base resins, a plurality of techniques have been disclosed.
Further, to prepare a curable resin composition where a higher electroconductivity is required, there is known a method of forming (or shaping) the curable resin composition, and then heating so as to carbonize and graphitize the resultant formed product (see, for example, JP-A-8-222241).
When a curable resin composition containing normal graphite powder is used, the amount of graphite powder added must be greatly increased so as to provide the same electroconductivity as the cured product according to the present invention. As a result, when such a composition containing normal graphite powder is used, not only the specific gravity of the formed product disadvantageously is increased but also the formability thereof is deteriorated at the time of the formation process such as compression molding, transfer molding or injection molding. Further, in the case of a composite material comprising a combination of a resin and normal graphite powder, a cured product having a contact resistance of 2xc3x9710xe2x88x922 xcexa9cm2 or less could not be obtained.
If the production process includes a step of heating the formed product to a high temperature of 1,000xc2x0 C. to 3,000xc2x0 C. for a long time for the purpose of obtaining a high electroconductivity, there arises a problem that the production takes a long time and that the production process becomes complicated so as to increase the production cost.
The present invention has been made under these circumstances and a main object of the present invention is to provide an electroconductive curable resin composition which is capable of providing a cured product having an excellent electroconductivity, a high heat resistance, a good heat-radiating property and a superior polymer processability, even when the curable resin composition contains a relatively small amount of electroconductive filler charged therein. This object also includes providing a cured product of such a electroconductive curable resin and a formed product using the curable resin composition.
Under these circumstances, the present inventors have made extensive investigations to develop an electroconductive curable resin composition comprising, as main starting materials, a graphite powder and a curable resin or a monomer composition therefor (if desired, further containing an initiator or the like), which can provide a cured product having an excellent electroconductivity, a high heat resistance and a good heat-radiating property. As a result, an electroconductive curable resin composition and a cured product achieving the object of the present invention have been accomplished by the combination of a specific graphite containing boron with a curable resin.
More specifically, the present invention relates to an electroconductive curable resin composition, a cured product thereof and a formed product using the curable resin composition, which typically include the following embodiments (1) to (17).
(1) An electroconductive curable resin composition comprising (A) a graphite powder containing boron in the graphite crystal, and (B) a curable resin and/or a curable resin composition, at a ratio of 20 to 99.9:80 to 0.1 in terms of the mass ratio of the component (A) to component (B) provided that the sum of the mass ratios of the components (A), (B) and (C) is 100.
(2) An electroconductive curable resin composition comprising (A) a graphite powder containing boron in the graphite crystal, (B) a curable resin and/or a curable resin composition, and (C) vapor-phase process carbon fiber having a fiber diameter of 0.05-10 xcexcm and a fiber length of 1-500 xcexcm, and/or carbon nanotube having a fiber diameter of 0.5-100 nm and a fiber length of 0.01-10 xcexcm.
(3) An electroconductive curable resin composition as described in the above item (2), wherein the mass ratio of the sum of the components (A) and (C) to the component (B), i.e., the mass ratio (A+C:B) is 20 to 99.9:80 to 0.1 provided that the sum of the mass ratios of the components (A), (B) and (C) is 100.
(4) An electroconductive curable resin composition as described in the above item (2) or (3), wherein the mass ratio of the component (A) to the component (C) is 60 to 99.9:40 to 0.1 provided that the sum of the mass ratios of the components provided that the sum of the mass ratios of the components (A) and (c) is 100.
(5) An electroconductive curable resin composition as described in any one of the above items (1) to (4), wherein the powder electric resistivity in the right angle direction of the graphite powder as the component (A) is 0.06 xcexa9cm or less with respect to the applied pressure direction, in a state where a pressure is applied to the graphite powder so as to provide a bulk density of the graphite powder of 1.5 g/cm3.
(6) An electroconductive curable resin composition as described in any one of the above items (1) to (5), wherein the component (A) has an average particle size of 5 to 80 xcexcm.
(7) An electroconductive curable resin composition as described in any one of the above items (1) to (6), wherein the component (A) is a graphite powder having a specific surface area of 3 m2/g or less, an aspect ratio of 6 or less, a tapping bulk density of 0.8 g/cm3 or more and a lattice spacing (Co value) of 6.745 xc3x85 or less.
(8) An electroconductive curable resin composition as described in any one of the above items (1) to (7), wherein the component (B) comprises at least one resin selected from a phenolic resin, an unsaturated polyester resin, an epoxy resin, a vinyl ester resin and an allyl ester resin; and a curing agent.
(9) An electroconductive curable resin composition as described in the above item (8), wherein the component (B) comprises an epoxy resin and a phenolic resin.
(10) An electroconductive curable resin composition as described in the above item (9), wherein the epoxy resin comprises a cresol novolak-type epoxy resin and the phenolic resin comprises a novolak-type phenolic resin.
(11) An electroconductive curable resin composition as described in the above item (8), wherein the component (B) comprises a vinyl ester resin and/or an allyl ester resin; at least one monomer selected from allyl ester monomer, acrylic acid ester monomer, methacrylic acid ester monomer and styrene monomer; and a radical polymerization initiator.
(12) An electroconductive curable resin composition as described in the above item (11), wherein the vinyl ester resin is a novolak-type vinyl ester resin.
(13) An electroconductive curable resin composition as described in any one of the above items (1) to (12), wherein the component (A) is a graphite powder containing from 0.05 to 5.0 mass % of boron.
(14) An electroconductive cured product which is obtainable by curing an electroconductive curable resin composition as described in any one of the above items (1) to (13), which has a volume resistivity of 2xc3x9710xe2x88x922 xcexa9cm or less, a contact resistance of 2xc3x9710xe2x88x922 xcexa9cm2 or less and a thermal conductivity of 1.0 W/mxc2x7K or more.
(15) A process for producing an electroconductive cured product as described in the above item (11), which comprises forming the cured product by any one of compression molding, transfer molding, injection molding and injection-compression molding.
(16) A separator for fuel cells, which is obtainable by curing an electroconductive curable resin composition as described in any one of the above items (1) to (13) which is an electroconductive curable resin composition comprising from 50 to 95 mass % of the component (A) (or, from 50 to 95 mass % of the sum of the component (A) and the component (C), if any), the separator having a volume resistivity of 2xc3x9710xe2x88x922 xcexa9cm or less, a contact resistance of 2xc3x9710xe2x88x922 xcexa9cm2 or less, a thermal conductivity of 1.0 W/mxc2x7K or more and a gas permeability of 1xc3x9710xe2x88x926 cm2/sec or less.
(17) A process for producing a separator for fuel cells, which comprises forming a separator for fuel cells by any one of compression molding, transfer molding, injection molding and injection-compression molding, the separator being obtainable by curing an electroconductive curable resin composition as described in any one of the above items (1) to (13) which is an electroconductive curable resin composition comprising from 50 to 95 mass % of the component (A) (or, from 50 to 95 mass % of the sum of the component (A) and the component (C), if any), and the separator having a volume resistivity of 2xc3x9710xe2x88x922 xcexa9cm or less, a contact resistance of 2xc3x9710xe2x88x922 xcexa9cm2 or less, a thermal conductivity of 1.0 W/mxc2x7K or more and a gas permeability of 1xc3x9710xe2x88x926 cm2/sec or less.